Sorta sounds like you want to "trace" the gear (vector) and not "mill" it in x-y (raster) fashion, eh? MACH2 will import a dxf as a vector file and let you do that as I recall Is that a hint? [My terms may be off - but you'll get the idea I bet]
I've used a variety of other programs to generate the vector to gCode - so I'm not intentionally being cute here - just can't recall what I did last that worked so good!
For example ALGOLAB has a raster to vector that will let you save as a dxf and then import into MACH2, so there's a path, certainly others will have some clearer insights too. cheers - Jim